1. Field of the Invention
This invention relates to a control circuit of panel brightness, and more particularly to a control circuit of panel brightness of Liquid Crystal Display (LCD).
2. Description of the Related Art
In notebooks, an Embedded Controller (EC) is for controlling panel brightness of a Liquid Crystal Display, such as DSTN LCD. The function of the Embedded Controller is similar to the function of a processor. With the program instruction codes of the Embedded Controller, EC helps to control multiple peripheral devices of the notebook. The above mentioned panel brightness control is only one of its functions.
Furthermore, the Embedded Controller is substantially a microprocessor, which controls Read Only Memory, Random Access Memory, Clock Generator, Registers, Input/Output devices, and so on, by instruction sets designed by a software program, and the Embedded Controller enables to execute the functions of data read/write, operation, storage, and so on. By using the Embedded Controller to execute the operation of a keyboard device in a notebook, it will cause the following problems. Firstly, it needs not only a complicate circuit producing process to manufacture the Embedded Controller, but also a software program to write an instruction set for the control operation of circuit components of the Embedded Controller. Moreover, in order to link the Embedded Controller with the external Basic Input/Output System (BIOS), manufacturers must also pay the royalty fee to get the license of instruction sets for controlling external Basic Input/Output System. The Embedded Controller may have similar function as a microprocessor, which includes more powerful and complicate functions compared with an ordinary logic circuit. However, it costs much more to produce the Embedded Controller than an ordinary logic circuit for manufactures.
Every manufacturer of Embedded Controllers designs different circuit and different software instruction sets. Every circuit performance of Embedded Controllers generated by different manufacturers is not all the same. Therefore, generally speaking, system manufacturers of notebooks are preferred to use products of a specific Embedded Controller manufacturer. But at this present, there are few manufacturers to produce Embedded Controllers, notebook system manufacturer cannot have much choice for the sources of Embedded Controllers. When there is more demand from system manufacturer than supply from manufactures of Embedded Controller, Embedded Controllers will be out of stock. Therefore it will badly affect the quantity and efficiency of producing notebooks for system manufacturers. Additionally, bigger system manufacturers always monopolize the sources of Embedded controllers. For smaller system manufacturers, the shortage situation will happen unpredictable, and the probability is more than bigger manufacturers. The influence on smaller manufacturers is more serious.
When Embedded Controllers are out of stock, the system manufacturers cannot help but change the variety of Embedded Controllers installed in notebooks. It means to buy Embedded Controllers from other Embedded Controller manufacturer. But as it is mentioned above, circuits and software instruction sets designed for one kind of Embedded Controller may not suitable for another kind of Embedded Controller. It makes performance of Embedded Controllers produced by each manufacturer not all the same. When the system manufacturers uses another kind of Embedded Controllers, they need to redesign a set of instruction codes for new electric components to control new Embedded Controllers, in order to execute required tasks. That increases much time and cost. Furthermore, even they have changed new Embedded Controllers, due to the limited source; there are not many choices. So the problem, that manufacturers might run out of stock, maybe still happen again. System manufacturers then cannot help but seek another supply of Embedded Controllers.
Therefore, it costs a lot to control panel brightness by using Embedded Controllers. The main reason is that the price of Embedded Controllers is very high, and the production of Embedded Controllers is limited in the world, which would easily cause shortage of stock. Besides, it needs to design additional instruction codes related to the Embedded Controller. It is rather inconvenient and time consuming.